This invention concerns a simple and compact apparatus for producing either chlorine gas or a hypochlorite compound.
Production of a chlorine releasing compound in the form of chlorine gas or a hypochlorite is important for a number of reasons including the use of disinfecting swimming pool water. Perhaps the most economical method of producing chlorine and hypochlorite compounds involves the application of an electric current to an alkali or alkaline earth metal chloride solution. In general, the resulting reaction yields the desired chlorine gas at the anode and hydrogen gas and an alkali or alkaline earth metal hydroxide at the cathode according to the following equation: EQU 2Na.sup.+ + 2Cl.sup.- + 2H.sub.2 O .fwdarw. 2Na.sup.+ + 2OH.sup.- + Cl.sub.2 + H.sub.2 ( 1)
present arrangements for producing chlorine gas in this manner typically employ pairs of electrodes disposed in separate cells containing salt (sodium chloride) brine solution. Other arrangements may employ a number of electrodes disposed in a single cell with the electrodes connected in parallel. In the latter arrangement, a fairly high D.C. current but low voltage must be applied to the electrodes to cause a chlorine gas producing reaction in the cell. The fairly high current is required since the electrodes are connected in parallel and a certain amount of current must be applied to each electrode before the gas producing reaction will take place. Along with the higher current requirement, a lower voltage is also required and this would be obtained from a conventional A.C. source using some type of step-down transformer. The combination of the high current requirement and a low voltage requirement gives rise to a need for fairly large conductors to carry the current, rectifiers having large current carrying capacity, and fairly large transformers for "stepping-down" the voltage.
The U.S. Pat. No. 3,835,020 issued Sept. 10, 1974, to Galneder, a chlorine producing apparatus is disclosed wherein the electrodes are connected in series and allegedly result in the production of chlorine, oxygen and hydrogen. No separation is made in the electrode chambers into anode and cathode compartments and hence all products produced as a result of electrolysis are vented by the same exit port. Since chlorine reacts readily with hydrogen to form hydrogen chloride it is questionable whether such an apparatus would produce any usable chlorine compound for purification purposes.
When using chlorine or a hypochlorite for water treatment purposes, there are a variety of chemical reactions that can and do take place. When chlorine gas is introduced into a water solution the chlorine molecule per se may interact with contaminants contained in the water supply. On the other hand, chlorine in water reacts according to Equation 2 to form hypohalous acid and hydrogen chloride: EQU Cl.sub.2 + 2H.sub.2 O .fwdarw. HOCl + HCl + H.sub.2 O (2)
hypohalous acid in turn reacts as shown in Equation 3 to form hydrogen chloride and nascent oxygen: EQU HOCl + H.sub.2 O .fwdarw. HCl + O.sub.2 + H.sub.2 O (3)
it is the interaction of the nascent oxygen with the contaminants in the water which brings about additional purification. Thus it can be readily seen that in many instances it is desirable to introduce chlorine gas directly into a water supply so that both chlorine and oxygen may be used for purification purposes.
On the other hand, it is often desirable to use a hypochlorite as the disinfecting or purification reagent. When the electrolysis products from Equation 1 are combined, chlorine reacts with sodium hydroxide or other alkali or alkaline earth metal hydroxides to form sodium hypochlorite or the appropriate alkali or alkaline earth metal hypochlorite and hydrogen chloride according to Equation 4: EQU H.sub.2 O + Cl.sub.2 + NaOH .fwdarw. NaOCl + HCl + H.sub.2 O (4)
the more alkaline the solution is the more rapid the conversion of chlorine into the hypochlorite will be. Sodium hypochlorite in aqueous solution forms sodium chloride and nascent oxygen according to Equation 5: EQU 2NaOCl + H.sub.2 O .fwdarw. 2NaCl + O.sub.2 + H.sub.2 O (5)
the oxygen released interacts with the contaminants in the water to oxidize them thereby bringing about water purification.